Helmut Ringsdorf provided a theoretical framework for the design of polymer conjugates of small molecule drugs over thirty years ago (See Ringsdorf, “Structure and Properties of Pharmacologically Active Polymers”, J. POLYMER SCI.: Symposium No. 51, 135-153 (1975)). While many conjugates have been synthesized and evaluated in animals, few have progressed to clinical trials and those trials have been largely disappointing. The identification of polymer drug conjugates that represent improvements over the parent small molecules remains an area of active research.
Fumagillin is a small molecule which has been used as an antimicrobial and antiprotozoal agent. Its physiochemical properties and method of production are well known (See U.S. Pat. No. 2,803,586 (Peterson, et al, incorporated herein by reference) and Turner, J. R. et al, The Stereochemistry of Fumagillin, Proc. Natl. Acad. Sci. 48, 733-735 (1962)). The fermentation product, fumagillin, may be hydrolyzed to yield the alcohol fumagillol which in turn may be converted into various derivatives including carbamoylfumagillol, MW 325. The synthesis and preparation of carbamoylfumagillol and some small molecule derivatives are described in U.S. Pat. No. 5,166,172.
Fumagillin and related compounds are believed to exert their biological effects through the inhibition of methionine aminopeptidase-2 (MetAP2), a metalloprotease. This enzyme removes N-terminal methionine from nascent cellular proteins. (See Tucker, L. A., et al “Ectopic Expression of Methionine Aminopeptidase-2 Causes Cell Transformation and Stimulates Proliferation”, Oncogene 27, 3967 (2008).)
Carbamoylfumagillol and derivatives as well as other inhibitors of MetAP2 have shown therapeutic benefits in preclinical and clinical studies. These compounds inhibit cell proliferation and angiogenesis as described in U.S. Pat. No. 5,166,172 (Kishimoto, et al, incorporated herein by reference). One of these derivatives, chloroacetylcarbamoylfumagillol (TNP-470) has been extensively studied. (See H. Mann-Steinberg, et al., “TNP-470: The Resurrection of the First Synthetic Angiogenesis Inhibitor”, Chapter 35 in Folkman and Figg, Angiogenesis: An Integrative Approach from Science to Medicine, Springer N.Y. (2008).) TNP-470 has shown activity against many cancers, including lung cancer, cervical cancer, ovarian cancer, breast cancer, and colon cancer. Because of dose-limiting neurotoxicity, TNP-470 has been tested using multiple dosing regimens, but these attempts to limit its toxicity have been unsuccessful. Thus, TNP-470 has been found to be too toxic for human use. With few exceptions, unacceptable weight loss or failure to gain weight was observed in animals receiving TNP-470. TNP-470 has a short half-life and requires extended intravenous administration for therapeutic use. A metabolite of TNP-470, carbamoylfumagillol has a half-life of 12 minutes in man. (See Herbst et al., “Safety and Pharmacokinetic Effects of TNP-470, an Angiogenesis Inhibitor, Combined with Paclitaxel in Patients with Solid Tumors: Evidence for Activity in Non-Small-Cell Lung Cancer”, Journal of Clinical Oncology 20(22) 4440-4447 (2002). In addition, fumagillin and its derivatives are hydrophobic and difficult to formulate.
Methionine aminopeptidase-2 (MetAP2), a metalloprotease, is an enzyme that processes N-terminal methionine from nascent cellular proteins. Inhibition of MetAP2 has been shown to block angiogenesis and suppress tumor growth in preclinical tumor models. Interestingly, fumagillin, chloroacetylcarbamoylfumagillol, carbamoylfumagillol and related compounds have been shown to be inhibitors of MetAP2. (See Tucker, L. A., et al. “Ectopic Expression of Methionine Aminopeptidase-2 Causes Cell Transformation and Stimulates Proliferation”, Oncogene 27, 3967 (2008).)